1. Field of the Invention
This invention relates broadly to cooling inlet air to a gas turbine.
2. Description of Related Art
A conventional gas turbine system includes: an air compressor for compressing the turbine inlet air; a combustion chamber for mixing the compressed air with fuel and combusting the mixture, thereby producing a combustion gas; and a power turbine that is driven by the combustion gas, thereby producing an exhaust gas and useful power.
Over the years, various technologies have been employed to increase the amount of useful power that the power turbine is able to produce. One way of increasing the power output of a gas turbine is to cool the turbine inlet air prior to compressing it in the compressor. Cooling causes the air to have a higher density, thereby creating a higher mass flow rate through the turbine. The higher the mass flow rate through the turbine, the more power the turbine produces. Cooling the turbine inlet air temperature also increases the turbine""s efficiency.
Various systems have been devised for chilling the inlet air to the compressor. One such system uses evaporative cooling, wherein ambient temperature water is run over plates or over a cellular media inside of a chamber, thereby creating thin films of water on each plate, or on the media. The turbine inlet air is then drawn through the chamber, and through evaporative cooling, the air is cooled to near the wet bulb temperature. This system is limited to cooling the air to the wet bulb temperature, which is dependent upon the atmospheric conditions at any given time. Another system uses a chiller to chill water that is then run through a coil. The inlet air is then drawn through the coil to cool the air. This system requires parasitic power or steam to drive the chilling system which has the further drawback that when inlet air cooling is needed the most, i.e. during the day when the temperature is the highest, is also the time when power demand from the turbine is the highest, i.e. during the day when power users are in operation. In order to run the chiller, power from the turbine is required, but this power is needed by the users of the turbines power. On the other hand, when cooling is needed the least, i.e. at night when the temperatures are the lowest, surplus power from the turbine is available because the consumers of the turbine""s power are largely not in operation. Accordingly, a continuing need exists for a turbine inlet air cooling system which: would efficiently cool turbine inlet air; would take advantage of surplus power available during times of low consumer power demand; and would not drain the system of power during times of high consumer power demand.
A. Inlet Air Cooling
Described in greater detail below is a method for chilling inlet air to a gas turbine power plant, which may include: providing a system of circulating chilling water including a chilling system; providing an inlet air chiller for lowering the temperature of the inlet air being fed to a gas turbine compressor through heat transfer between the circulating chilling water and the inlet air, providing a thermal water storage tank which is operably connected to the system of circulating chilling water, the thermal water storage tank containing chilling water having a bottom; during a charge cycle, removing a first portion of chilling water from the thermal water storage tank, passing the removed first portion of water through the chilling system to lower the temperature of the removed first portion of water and to provide a chilled removed first portion of water, and then introducing the chilled removed first portion of water into the thermal water storage tank at a point proximate the bottom of the tank, wherein the chilled removed first portion of water is introduced to the tank in an amount sufficient to lower the average temperature of the chilling water in the thermal water storage tank; and during a discharge cycle, chilling the inlet air by removing a second portion of chilling water from the thermal water storage tank, from a point proximate the bottom of the tank and then passing the second portion of chilling water to the inlet air chiller to make heat transfer contact between the second portion of chilling water and the inlet air, such that the temperature of the inlet air is lowered.
In another method that is described herein, the average temperature of the chilling water in the tank may be lowered to about 33xc2x0 F. to about 40xc2x0 F. during the charge cycle and may be raised to about 60xc2x0 F. to about 70xc2x0 F. during the discharge cycle. In another specific embodiment, the times of the charge and discharge cycles may be such that, before the temperature of the chilling water proximate the bottom of the tank reaches about 36xc2x0 F. during the discharge cycle, the charge cycle is initiated. In another specific embodiment of the method for chilling inlet air, the first portion of chilling water removed from the thermal water storage tank during the charge cycle may be removed through a top outlet. In yet another specific embodiment, the chilling water in the tank may have an average temperature that can be lowered during the charge cycle and raised during the discharge cycle. In a further specific embodiment of the claimed method, the discharge cycle may be carried out during the night-time and the charge cycle may be carried out during the day-time. In still another specific embodiment, the water level in the tank may remain substantially constant during the charge and discharge cycles. In still a further specific embodiment, the one or more chillers may be deactivated during the discharge cycle. In another specific embodiment, the discharge cycle may occur during peak power usage of the gas turbine power plant. In another specific embodiment, the discharge cycle may be performed after the removing of at least a portion of the volume of chilling water from the thermal water storage tank during the charge cycle, such that the chilled removed water that is introduced into the thermal water storage tank at a point proximate the bottom of the tank may remain substantially at the point proximate the bottom of the tank. In another specific embodiment, the first portion of chilling water removed during the charge cycle may be sufficient to chill substantially all of the water in the thermal water storage tank to a temperature below the temperature of maximum water density. In yet another specific embodiment of the claimed method, the second portion of chilling water removed during the discharge cycle may be substantially all of the chilling water in the tank. In a further specific embodiment of the method of the present invention, the thermal water storage tank contains a volume of chilling water that is sufficient to lower the temperature of the inlet air to a range of from about 45xc2x0 F. to about 55xc2x0 F. for a period of between about 4 hours to about 12 hours.
Also described herein is a method of chilling water delivered to the air chiller in a gas turbine power plant system having at least one air chiller for lowering the temperature of inlet air, at least one air compressor for compressing the inlet air, at least one combustor for burning the compressed air and providing combustion gas, and at least one power turbine driven by the combustion gas for producing useful power, a method of chilling water delivered to the air chiller, the method including the steps of: providing the at least one air chiller with an air chiller inlet that may receive water, and an air chiller outlet that may expel water; providing a thermal water storage tank, having a bottom portion, a top portion, at least one bottom opening proximate the bottom portion and at least one top opening proximate the top portion, and containing a volume of stored water having an average temperature, and temperature of maximum water density; performing a charge cycle, by introducing through the at least one bottom opening a first quantity of chilled water which has a chilled water temperature that is below the temperature of maximum water density, thereby lowering the average temperature of the volume of stored water, wherein the first quantity of chilled water being introduced through the bottom opening is sufficient to lower the average temperature of the volume of stored water to a temperature that is below the temperature of maximum water density; and performing a discharge cycle by removing a second quantity of chilled water from the tank through the at least one bottom opening and passing the second quantity of chilled water to the air chiller inlet, to lower the temperature of the inlet air, thereby raising the temperature of the second quantity of chilled water and providing high temperature water, then introducing the high temperature water to the at least one top opening in the tank.
In yet another method of chilling water, the temperature of maximum water density may be from about 20xc2x0 F. to about 39.2xc2x0 F. In another specific embodiment, the temperature of maximum water density may be about 39.2xc2x0 F. In another specific embodiment, the temperature of the stored water may have a temperature of from about 34xc2x0 F. to about 40xc2x0 F. In yet another specific embodiment of the claimed method the temperature of the stored water may have a temperature corresponding to the maximum water density of about 39.2xc2x0 F. In another specific embodiment sodium nitrate may be added to depress the freezing temperature of the water thereby allowing stored water to be in the range of about 25xc2x0 F. to about 34xc2x0 F. In another specific embodiment of the method of the present invention, the useful power produced by the power turbine may be consumed at a variable rate, and the charge cycle may be performed when the rate is at a minimum. In a further specific embodiment, the useful power produced by the power turbine may be consumed at a variable rate, and the discharge cycle may be performed when the rate is at a maximum. In yet another specific embodiment of the method of the present invention, the quantity of water expelled during the discharge cycle may be less than the volume of stored water. In a further specific embodiment, the quantity of chilled water may be chilled by passing water through at least one chiller. In still another specific embodiment of the claimed method, the temperature of inlet air may be lowered from a high temperature of from about 85xc2x0 F. to about 95xc2x0 F. to a low temperature of from about 45xc2x0 F. to about 55xc2x0 F. In still a further specific embodiment, the high temperature may be about 90xc2x0 F. and the low temperature may be about 50xc2x0 F. In yet another specific embodiment, the output of the gas turbine power plant system may be from about 50 megawatts to about 250 megawatts.
Also described below is a gas turbine power plant system, wherein the system includes: one or more air chillers for lowering the temperature of inlet air; one or more air compressors for compressing the inlet air; one or more combustors for burning the compressed air and providing combustion gas; and one or more power turbines driven by the combustion gas for producing useful power, and an improvement that may include: a thermal water storage tank for containing chilled water, wherein the thermal water storage tank has a bottom portion with a bottom outlet and a top portion, and the tank is operably connected to the air chiller such that the chilled water passes from the bottom outlet to the air chiller to lower the temperature of the inlet air and is returned to the thermal water storage tank; and a water chilling system for chilling the water in the thermal water storage tank, wherein the water chilling system is configured to receive high temperature water from the top portion of the tank, and wherein the system is configured to introduce low temperature water to the bottom portion of the tank, such that the average temperature of the water in the tank is lowered; and wherein the water chilling system includes one or more chillers for lowering the temperature of the high temperature water from the top portion of the tank to provide low temperature water.
In an example of such a gas turbine power plant system, the thermal water storage tank may have a bottom, and the bottom outlet may be positioned at a height that is less than about 10 feet from the bottom of the tank. In another specific embodiment of the gas turbine power plant system, the thermal water storage tank may have a bottom, and the bottom outlet may be positioned at a height that is less than about 5 feet from the bottom of the tank. In another specific embodiment, the thermal water storage tank may have a bottom, and the bottom outlet may be positioned at a height that is less than about 18 inches from the bottom of the tank. In another specific embodiment, the tank may have a top outlet and a bottom inlet such that, in a charge cycle the high temperature water may be removed through the top outlet and may be fed to the one or more chillers, and the low temperature water may be introduced to the tank through the bottom inlet. In a further specific embodiment of the gas turbine power plant system, the tank may have a bottom outlet such that, in a discharge cycle, chilling water may be removed from the tank through the bottom outlet. In still a further specific embodiment of the gas turbine power plant system, the tank may have a bottom outlet such that, in a discharge cycle, chilling water may be removed from the tank through the bottom outlet, fed to the air chiller and is returned to the tank, bypassing the one or more chillers of the water chilling system. In still a further specific embodiment of the gas turbine power plant system, the top portion may be separated from the bottom portion by a thermocline.
In yet another example, during the charge cycle, the bottom inlet may receive a quantity of chilled water that is sufficient to supply the air chiller with water having a temperature below the temperature of maximum water density for four or more hours. In another specific embodiment, during the charge cycle, the bottom inlet may receive a quantity of chilled water that is sufficient to supply the air chiller with water having a temperature below the temperature of maximum water density for eight or more hours. In still another embodiment, during the charge cycle, the bottom inlet may receive a quantity of chilled water that is sufficient to supply the air chiller with water having a temperature below the temperature of maximum water density for twelve or more hours.
In still another example, the thermal water tank may have a height of from about 25 feet to about 70 feet. In yet another specific embodiment, the thermal water tank may have a diameter of from about 50 feet to about 250 feet. In another specific embodiment, the thermal water tank may have a diameter, and a height, and the diameter may be greater than the height. In yet another specific embodiment of the claimed invention, the volume of stored water may be greater than about eight hundred thousand gallons. In still a further specific embodiment, the temperature of the water in the top portion may be about 15xc2x0 F. to about 35xc2x0 F. greater than the temperature of the water in the bottom portion. In another specific embodiment, the thermal water storage system may include a plurality of thermal water storage tanks, each of the plurality of tanks may have a bottom inlet and a bottom outlet, and each of the plurality of tanks may have a top inlet and a top outlet. In another specific embodiment, the bottom inlet may have a bottom diffuser, and the top inlet may have a top diffuser, whereby the water entering the bottom inlet is diffused, and the water entering the top inlet may be diffused. In yet another specific embodiment, the temperature of the water in the top portion of the tank may have a temperature ranging from about 60xc2x0 F. to about 70xc2x0 F. In still a further specific embodiment, the temperature of the water in the bottom portion of the tank may have a temperature that is above the freezing temperature. In another specific embodiment, the water chilling system may include at least one mechanical chiller. In still another specific embodiment of the present invention, the water chilling system may include at least one absorption chiller. In still a further specific embodiment, the water chilling system may include at least one mechanical chiller and at least one absorption chiller. In yet another specific embodiment, the mechanical chiller may receive chilled water from the absorption chiller, and the mechanical chiller may further chills the chilled water. In another specific embodiment, the gas turbine power plant system may additionally including a heat recovery steam generator and a steam turbine, wherein the absorption chiller may be driven by steam from the heat recovery steam generator. Another specific embodiment of the gas turbine power plant system may additionally include a heat recovery steam generator and a steam turbine, wherein the absorption chiller is driven by back pressure from the steam turbine exhaust. In another specific embodiment, the inlet air may be lowered from a first temperature of about from 85xc2x0 F. to about 95xc2x0 F. to a second temperature of from about 45xc2x0 F. to about 55xc2x0 F. in the inlet air chiller. In yet another embodiment, the first temperature may be about 90xc2x0 F. and the second temperature may be about 50xc2x0 F. In another specific embodiment of the gas turbine power plant system, the chilling water being fed to the inlet air chiller may have a temperature of from about 34xc2x0 F. to about 40xc2x0 F. In another specific embodiment, the gas turbine power plant system may additionally include a steam turbine and a heat recovery steam generator, and the heat recovery steam generator may receive exhaust gas from the power turbine and may provide high pressure steam to the steam turbine, and the steam turbine may provide low pressure steam.
B. Additional Methods and Systems
Embodiments of the invention additionally include passing inlet air through a cooling coil that includes an opening for receiving the inlet air and that is operably connected to a gas turbine power plant. The gas turbine power plant may include at least one gas turbine, and at least one gas turbine inlet which receives the inlet air. The method may further include passing circulating water through a water chiller at a first flow rate to reduce the temperature of the circulating water, the water chiller including a conduit through which the circulating water is capable of passing and passing the circulating water having the first flow rate through the cooling coil in an amount sufficient to lower the temperature of the inlet air. Additionally, the method may include reducing the flow rate of the circulating water passing through the water chiller, passing the circulating water through a water chiller at a second flow rate to reduce the temperature of the circulating water, the second flow rate being lower than the first flow rate, and passing the circulating water having the second flow rate through the cooling coil in an amount sufficient to lower the temperature of the inlet air.
Additional embodiments may include providing a system of circulating liquid chilling water including a chilling system that includes a first mechanical chiller and a second mechanical chiller, the first and second mechanical chillers being arranged in series and passing at least a portion of the liquid chilling water through the first mechanical chiller and the second mechanical chiller, the liquid chilling water passing through the first mechanical chiller being lowered to a first temperature, and the liquid chilling water passing through the second mechanical chiller being lowered to a second temperature that is lower than the first temperature, thus providing a staged liquid chilling water temperature drop, wherein the staged liquid chilling water temperature drop is from about 20xc2x0 F. to about 34xc2x0 F. The method may further include providing an inlet air chiller, comprising a cooling coil through which liquid chilling water passes, for lowering the temperature of inlet air being fed to the compressor through heat transfer between the liquid chilling water passing through the cooling coil and the inlet air, wherein the inlet air chiller provides a liquid chilling water temperature rise of from about 20xc2x0 F. to about 34xc2x0 F. and chilling the inlet air by directing the liquid chilling water to the inlet air chiller and passing the liquid chilling water through the cooling coil of the inlet air chiller to make heat transfer contact between the liquid chilling water and the inlet air. Preferably, the method additionally includes adding potassium formate to the circulating water in an amount sufficient to depress the freezing point of the circulating water. In the alternative, or additionally, the method may include contacting the inlet air leaving the cooling coil with a control system, a temperature sensor, and a relative humidity sensor to monitor the leaving air temperature and relative humidity of the leaving air and varying the flow or the temperature of the circulating water to maintain a relative humidity of the coil to below about 95% to about 99% RH for optimal efficiency in a combined cycle system.
Additional embodiments may include a system for chilling inlet air for a gas turbine power plant including passing inlet air through a cooling coil that includes an opening for receiving the inlet air and that is operably connected to a gas turbine power plant that includes at least one gas turbine, and at least one gas turbine inlet which receives the inlet air, passing circulating water through a water chiller at a first flow rate to reduce the temperature of the circulating water, the water chiller including a conduit through which the circulating water is capable of passing and passing the circulating water having the first flow rate through the cooling coil in an amount sufficient to lower the temperature of the inlet air to a desired air temperature setpoint. The system may further include reducing the flow rate of the circulating water passing through the water chiller during lower ambient off-design periods to maintain the desired air temperature setpoint, passing the reduced flowrate circulating water through the water chiller at a second flow rate and reducing the temperature of the circulating water to maintain the desired air temperature setpoint, the second flow rate being lower than the first flow rate and passing the circulating water having the second flow rate through the cooling coil in an amount sufficient to lower the temperature of the inlet air to the desired air temperature setpoint. The method may additionally include reducing the flow rate of the circulating water passing through the two or more sequentially positioned compressors during lower ambient off-design conditions to maintain a higher circulating water delta T thereby allowing warmer water to pass through the upstream compressor thus improving the efficiency at partial load.
Certain embodiments include passing the circulating water through a heater prior to passing the circulating water through the cooling coil, in which the circulating water temperature is increased to a temperature that is higher than the temperature of the circulating water leaving the cooling coil and higher than the temperature of the air entering the cooling coil to maintain the minimum desired leaving air temperature.
Certain embodiments include adding an additive to the circulating water in an amount sufficient to depress the freezing point of the circulating water. Certain embodiments may further include adding an additive to the circulating water in an amount sufficient to depress the freezing point of the circulating water and minimizing any negative performance derating due to the additive effect on the heat transfer properties of water. Certain embodiments may include adding a salt additive to the circulating water in an amount sufficient to depress the freezing point of the circulating water. The salt additive may be added to the circulating water in an amount sufficient to depress the freezing point of the circulating water to a point that would specifically provide for protection of the system during low ambient temperature operation and to protect the system during shut-down periods. Certain embodiments may include adding sodium nitrate to the circulating water in an amount sufficient to depress the freezing point of the circulating water. In yet other embodiments, the method includes adding potassium formate to the circulating water in an amount sufficient to depress the freezing point of the circulating water.
In certain embodiments, the method includes determining a set point and reducing the flow rate of the circulating water passing through the water chiller when the temperature difference between the circulating water entering the cooling coil and the circulating water leaving the cooling coil reaches the set point. Certain embodiments include determining a leaving chilled water temperature set point and increasing the setpoint at reduced off-design ambient temperatures to maintain the desired air temperature off the coil until the temperature difference between the circulating water entering the cooling coil and the circulating water leaving the cooling coil reaches a minimum set point and reducing the flow rate of the circulating water passing through the water chiller and reducing the leaving chilled water temperature setpoint to maintain the desired air temperature off the coil.
Certain embodiments include passing the circulating water through a pump prior to passing the circulating water through the water chiller. In yet other embodiments, the method includes passing the circulating water through a pump prior to passing the circulating water through the water chiller, reducing the circulating water flowrate, and decreasing the temperature of the circulating water to maintain the desired leaving air temperature. Certain embodiments include passing the circulating water through one or more pumps and reducing the flow rate of the circulating water by shutting off at least one of the one or more pumps. Optionally, the method may include passing the circulating water through one or more pumps mounted in parallel and reducing the flow rate of the circulating water by shutting off at least one of the one or more pumps during partial load conditions. In yet other embodiments, the method includes passing the circulating water through one or more pumps and reducing the flow rate of the circulating water by lowering the speed (RPM) of the pump via a variable frequency drive on the one or more pump motors.
In certain embodiments, the gas turbine inlet air temperature leaving the cooling coil is about 40xc2x0 F. to about 60xc2x0 F. Certain embodiments include providing a temperature sensor contacting the inlet air leaving the cooling coil to monitor the inlet air temperature. In yet other embodiments, the method includes providing a temperature sensor contacting the inlet air leaving the cooling coil to monitor the inlet air temperature and lowering the temperature of the inlet circulating water when the inlet air temperature increases above the setpoint. In certain other embodiments, the method includes providing a wet bulb temperature sensor to monitor the ambient air wet bulb temperature entering the cooling coil. In yet other embodiments, the method includes providing a control system and a temperature sensor contacting the inlet air leaving the cooling coil to monitor the inlet air temperature and lowering the circulating water flowrate when the temperature difference between the circulating water entering the cooling coil and the circulating water leaving the cooling coil decreases to from about 50% to about 90% of the difference between the ambient air wet bulb temperature entering the cooling coil and the temperature of the leaving air.
In certain embodiments, the chilled water temperature entering the cooling coil is about 34xc2x0 F. to about 45xc2x0 F. In certain embodiments, the cooling coil includes a multipass cooling coil. In other embodiments, the cooling coil includes a four pass cooling coil. In yet other embodiments, the cooling coil includes a six pass cooling coil.
In certain embodiments, the water chiller includes an evaporator. Certain embodiments additionally include providing a thermal water storage tank which is operably connected to the water chiller. In yet other embodiments, the method includes providing a thermal water storage tank which is operably connected to the water chiller and during a charge cycle, removing a first portion of circulating water from the thermal water storage tank, passing the removed first portion of water through the water chiller to lower the temperature of the removed first portion of circulating water and to provide a chilled removed first portion of water, and then introducing the chilled removed first portion of water into the thermal water storage tank, wherein the chilled removed first portion of water is introduced to the tank in an amount sufficient to lower the average temperature of the circulating water in the thermal water storage tank. Certain embodiments include providing a thermal water storage tank which is operably connected to the water chiller and during a discharge cycle, chilling the inlet air by removing a second portion of water from the thermal water storage tank and then passing the second portion of water to the inlet cooling coil to make heat transfer contact between the second portion of the circulating water and the inlet air, such that the temperature of the inlet air is lowered.
Certain embodiments include controlling the inlet air temperatures of multiple gas turbines by throttling the flow of circulating water to the cooling coil of the gas turbine which has the lowest turbine inlet air temperature. In yet other embodiments, the method includes controlling the inlet air temperatures of multiple gas turbines by throttling the flow of circulating water to the cooling coil of the gas turbine which has the lowest turbine inlet air temperature and resetting the supply circulating water setpoint higher once the last gas turbine circulating water is throttled to maintain the desired turbine inlet air temperature until at least one of the gas turbines meets the desired inlet air temperature without throttling more than about 25% of fully open.
Additional embodiments include passing inlet air through a cooling coil, passing circulating water through a water chiller to reduce the temperature of the circulating water and to provide chilled water, passing the chilled water through the cooling coil to lower the temperature of the inlet air and to provide chilled inlet air and supplying water in a fog to the chilled inlet air downstream of the cooling coil in an amount sufficient to supersaturate the already saturated chilled inlet air.
Certain embodiments include removing a portion of water from the inlet air via the condensate off of the cooling coil and then reintroducing that water through a high pressure spray or fog to the chilled inlet air. In yet other embodiments, the method includes providing a compressor within the gas turbine power plant, in which supplying water (fog) to the chilled inlet air includes entraining water in the chilled inlet air in an amount sufficient to lower the temperature of at least one stage of the compressor. In certain embodiments, the method includes passing the chilled inlet air through a compressor to vaporize the water in the chilled inlet air and cool interstages of the compressor. In certain embodiments, the chilled inlet air is at a saturation level. In certain embodiments, the chilled inlet air is at a supersaturation level after the water is supplied. The method may additionally include removing a portion of water from the inlet air via the condensate off of the cooling coil to be stored until thye chilling system is off and then reintroducing that water to be evaporated in the airstream by means of a high pressure spray or fog and thereby achieving evaporative cooling to near the wetbulb temperature.